Hydraulic coupling for vehicle drivetrain

ABSTRACT

A control valve (80) of a hydraulic coupling (32) controls pumping from a casing inlet port (58) by a hydraulic pump (48) through a casing outlet port (78) to control coupling between two rotary members such as by operation of a clutch (68). The casing (34) is connected to one of the rotary members while a pumping component embodied by an impeller (50) is connected to the other rotary member and meshed with an internal ring gear (54) having one more tooth than the number of impeller teeth to provide sufficient pumping capacity so that the pump can act as a brake while still having relatively constant pumping pressure. The control valve (80) includes an elongated valve element (82) mounted within a recess (98) to provide accurate control of its closure when the pumped hydraulic fluid reaches a predetermined pressure corresponding to a predetermined extent of relative rotation between the two drivetrain members. This elongated valve element (82) is made from a bimetallic strip so as to be temperature compensated and the outlet port (78) is provided with a main passage (94) as well as a bleed passage (96,96&#39;) that is cleaned when the valve element is opened. One construction has a valve body defining both the main passages (94) and the bleed passage (96) of the port, while another construction has the valve body defining the main passage (94) and the valve element (82) defining the bleed passage (96&#39;). Another construction has the recess (98) provided with an inclination extending from the port (78) and has a flat elongated valve element (82) that may be either straight or curved.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 482,761, nowU.S. Pat. No. 5,595,214, filed on Jun. 7, 1995 in the names of TheodoreE. Shaffer and Murat N. Okcuoglu as a continuation-in-part of priorapplication Ser. No. 08/205,900, now U.S. Pat. No. 5,536,215, filed onMar. 3, 1994 in the names of Murat N. Okcuoglu and Theodore E. Shafferas a continuation-in-part of prior application Ser. No. 08/016,168 filedon Feb. 10, 1993 in the name of Murat N. Okcuoglu and Theodore E.Shaffer, now U.S. Pat. No. 5,310,388.

TECHNICAL FIELD

This invention relates to a hydraulic coupling for use with a vehicledrivetrain within a housing thereof containing hydraulic fluid torotatively couple a pair of rotary members about a rotational axis.

BACKGROUND ART

Hydraulic couplings have previously utilized hydraulic pumps to couplerotary members of a vehicle drivetrain. For example, U.S. Pat. No.4,012,968 Kelbel discloses a differential mechanism wherein a hydraulicpump of the gerotor type is located radially outward from the axis ofrotation of the two members and provides pumped hydraulic fluid to aclutch that controls operation of a bevel type planetary gear set tolimit the differential action so as to thus have a limited slipfunction. U.S. Pat. No. 4,730,514 Shikata et al discloses anotherdifferential mechanism wherein a hydraulic pump controls operation of abevel gear type planetary gear set that extends between two rotarymembers such that a limited slip function of the differential gearoperation is also provided. Furthermore, U.S. Pat. Nos. 3,748,928Shiber; 4,719,998 Hiramatsu et al; 4,719,998 Hiramatsu et al; 4,727,966Hiramatsu et al; and 4,909,371 Okamoto et al disclose hydraulic pumpsutilized within vehicle drivetrains to control actuation of a clutchthat connects two rotary members of a vehicle drivetrain.

DISCLOSURE OF INVENTION

An object of the present invention is to provide an improved controlvalve for use in controlling rotative coupling of a pair of rotarymembers of a vehicle drivetrain.

In carrying out the above object, the control valve includes a valveelement and a port through which pressurized hydraulic fluid selectivelyflows to control the coupling of the pair of rotary members. The portincludes a main passage and a bleed passage that is communicated withthe main passage. The valve element of the control valve is mounted formovement between an open position spaced from the main passage of theport and a closed position where the valve element closes the mainpassage of the port but permits pressurized hydraulic fluid to bleedthrough the bleed passage, and the bleed passage upon subsequentmovement of the valve element to the open position is cleaned by fluidflow through both passages of the port.

In the preferred construction, the control valve has the valve elementconstructed as an elongated valve element having one portion that ismounted in a spaced relationship to the port and having a distal endthat is movable between the open position spaced from the main passageof the port and the closed position that closes the main passage of theport but allows hydraulic fluid to bleed through the bleed passage. Thiselongated valve element is preferably constructed from a bimetallicstrip so as to adjust for temperature changes during use.

The control valve has a valve body including an elongated mountingrecess having one location at which the one portion of the elongatedvalve element is mounted and having an end at which the main passage ofthe port extends through the valve body. In one construction, the valvebody defines the main passage of the port and also defines the bleedpassage of the port. In another construction, the valve body defines themain passage of the port and the distal end of the valve element definesthe bleed passage of the port.

The elongated valve element is disclosed in different constructions ashaving both a straight shape and a curved shape.

In one construction of the control valve, the valve body has anelongated mounting recess having one portion at which the one portion ofthe elongated valve element is mounted and has an end at which the mainpassage of the port extends through the valve body, and the valveelement has a generally flat shape between the one portion and itsdistal end. The recess in this construction has a greater depth at theend thereof than at said portion thereof and is inclined therebetween.The recess has a curved surface providing its inclination between itsone end and said one portion thereof where the valve element is mountedon the valve body. A connector is also disclosed for securing the valvebody for use. This connector may be provided by an adhesive or one ormore mechanical fasteners. The valve body is advantageously constructedas a plastic injection molding.

One construction of the control valve that is particularly adaptable foruse in a supercharged circuit with a pair of the ports and has its valvebody provided with an elongated mounting recess of a curved shapeincluding opposite ends and a curved intermediate portion extendingbetween its ends. The valve element in this construction is generallyflat and has a pair of opposite ends as well as a curved intermediateportion extending between its ends and mounted within the recess at thecurved intermediate portion of the recess. Each of the pair of ports hasthe same construction and the main passage of each port extends throughthe valve body at an associated end of the recess, and the recess has agreater depth at each end thereof than at the intermediate portionthereof and is inclined from each end thereof to its intermediateportion. This recess preferably has curved surfaces providing theinclination between each end thereof and its intermediate portion.Furthermore, like the straight construction of the control valve, thecurved control valve is also disclosed as including a connector forsecuring the valve body for use. Likewise, the connector can be eitheran adhesive or one or more mechanical fasteners and the construction ofthe control valve is advantageously made as a plastic injection moldingwith the recess having curved surfaces providing the inclination betweeneach end thereof and its intermediate portion.

The objects, features and advantages of the present invention arereadily apparent from the following detailed description of the bestmodes for carrying out the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view taken through one embodiment of a hydrauliccoupling including a control valve constructed in accordance with thepresent invention and operable to couple a pair of rotary members by ahydraulic pump having an associated clutch for limiting differentialoperation of a planetary gear set embodied by a bevel type differential;

FIG. 2 is a sectional view taken through the pump along the direction ofline 2--2 in FIG. 1 and discloses the pump as having an impeller withsix teeth meshed with an internal ring gear having seven teeth toprovide a pumping action that allows the pump to function as a brakewhile still having relatively constant pumping pressure that facilitatesactuation of the associated clutch without fluid pressure pulsation;

FIG. 3 is a view similar to FIG. 2 to illustrate that the pump can alsohave its impeller provided with five teeth and its internal ring gearprovided with six teeth when a greater pumping capacity is desired;

FIG. 4 is a view similar to FIGS. 2 and 3 but illustrating the impelleras having seven teeth and the internal ring gear as having eight teethwhen a more constant fluid pressure is desired;

FIG. 5 is an exploded perspective view illustrating the construction ofinlet valves for inlet ports through which hydraulic fluid is pumpedinto a casing of the coupling;

FIG. 6 is a sectional view taken along the direction of line 6--6 inFIG. 5 to illustrate the opening and closing valve operation;

FIG. 7 is a longitudinal view taken along the direction of line 7--7 inFIG. 1 to illustrate the control valve which is constructed according tothe invention and is associated with an outlet port through which thehydraulic fluid is pumped from the casing and whose operation controlsthe coupling of the rotary members to each other;

FIG. 8 is a sectional view taken along the direction of line 8--8 inFIG. 7 and further discloses a valve closure which closes the valve whenthe casing rotates above a predetermined speed;

FIG. 9 is a sectional view taken along the direction of line 9--9 inFIG. 7 to further illustrate the control valve and valve closureconstruction;

FIG. 10 is a partial sectional view that further illustrates theconstruction of the control valve at the outlet with a valve elementthereof shown in a solid line indicated open position and a phantom lineindicated closed position with respect to the outlet port;

FIG. 11 is a perspective view that further illustrates the constructionof the outlet port and the valve;

FIG. 12 is a sectional view similar to FIG. 1 of a related embodiment ofthe hydraulic coupling having the control valve of this invention andwherein the hydraulic pump functions as a brake upon the valve closingsuch that braking action provides the sole coupling operation thatlimits differential action of the associated planetary gear set;

FIG. 13 is a view similar to FIG. 1 of another embodiment of thehydraulic coupling having the control valve of this invention and whichhas a construction having particular utility for use in a vehicletransfer case to connect front and rear axles;

FIG. 14 is a view similar to FIG. 1 of another embodiment of thehydraulic coupling having the control valve of this invention and whichincludes a pair of hydraulic pumps and associated clutches thatrotatively couple a pair of rotary members of the associated drivetrainupon the valve closing;

FIG. 15 is an enlarged sectional view illustrating the transfer port andassociated check valve through which the hydraulic fluid is pumped tothe clutch actuating piston;

FIG. 16 is a partial perspective view that further illustrates thetransfer port check valve in its closed position;

FIG. 17 is a partial perspective view similar to FIG. 16 but with thetransfer port check valve shown in its open position;

FIG. 18 is an axial view of one construction of an actuating piston ofthe clutch;

FIG. 19 is a sectional view of the actuating piston taken along thedirection of line 19--19 in FIG. 18;

FIG. 20 is a perspective view illustrating the control valve outlet portwhich includes a main passage and a bleed passage and which is mountedwithin a recess;

FIG. 21 is a sectional view taken through the control valve generally inthe direction of line 21--21 in FIG. 20 and also illustrates the valveelement that controls fluid flow through the port illustrated;

FIG. 22 is a view similar to FIG. 1 of another embodiment which includesa supercharged circuit of pumped fluid between the hydraulic pump andthe clutch;

FIG. 23 is a partial view that illustrates a valved transfer port of thesupercharged circuit;

FIG. 24 is a view that illustrates the control valve for the outlet portof the supercharged circuit;

FIG. 25 is a schematic view that illustrates the fluid flow of thesupercharged circuit;

FIG. 26 illustrates the manner in which the transfer port and thecontrol valve of the hydraulic coupling can be tuned to have thetransfer port of a smaller size than the outlet port controlled by thecontrol valve;

FIG. 27 is a view that illustrates the manner in which the hydrauliccoupling can be tuned to have the transfer port the same size as theoutlet port controlled by the control valve;

FIG. 28 illustrates the manner in which the hydraulic coupling can betuned to have the transfer port larger than the outlet port controlledby the control valve;

FIG. 29 is a sectional view similar to FIG. 10 of a modifiedconstruction of the control valve;

FIG. 30 is a perspective view similar to FIG. 11 but with the modifiedconstruction of the control valve;

FIG. 31 is a partial view illustrating the distal end of the valveelement which defines the bleed passage of the outlet port;

FIG. 32 is an exploded sectional view taken in the same direction asFIG. 29 through another embodiment of the control valve wherein thevalve element is flat and has an elongated straight shape and whereinthe valve body has a recess whose port end is deeper than the locationat which the valve element is mounted;

FIG. 33 is an exploded perspective view that further illustrates theembodiment of FIG. 32 which is mounted for use as illustrated in both ofthese views by an adhesive that is provided on a film;

FIG. 34 is a sectional view of a further modification of the controlvalve taken in the same direction as FIG. 32 and having the sameconstruction except for mounting thereof that is provided by mechanicalfasteners illustrated as being injection molded with the valve body;

FIG. 35 is a view similar to FIG. 25 illustrating a further version ofthe supercharged circuit wherein the control valve of this invention isconstructed to control a pair of ports;

FIG. 36 is an exploded perspective view of the control valve of FIG. 35;

FIG. 37 is a sectional view taken along the curved line 37--37 of FIG.35 in an exploded manner to further illustrate the construction of thecontrol valve whose valve body is illustrated as being secured by anadhesive on a film; and

FIG. 38 is a sectional view of a further embodiment of the control valvetaken in the same direction as FIG. 37 and having the same constructionexcept for mounting thereof that is provided by mechanical fastenersillustrated as being injection molded with the valve body.

BEST MODES FOR CARRYING OUT THE INVENTION

With reference to FIG. 1 of the drawings, a partially illustratedvehicle drivetrain that is generally indicated by 20 includes adifferential 22 that is rotatively driven from the vehicle engine by arotary drive member 24 and operates to drive a pair of axial half shafts26 and 28 that respectively embody a pair of rotary members which rotateabout a rotational axis A. The differential includes a housing 30 forcontaining hydraulic fluid and having suitable unshown seals throughwhich the rotary members 24, 26 and 28 project. Within the housing 30,the differential includes a hydraulic coupling 32 that operates torotatively couple the axial half shafts 26 and 28 driven by the rotarydrive member 24 as is hereinafter more fully described.

With continuing reference to FIG. 1, the hydraulic coupling 32 includesa casing 34 of a hollow construction that is rotatable within thehousing about the rotational axis A and connected to one of the rotarymembers, which in the illustrated embodiment is the right axle halfshaft 26, with the connection being provided by a planetary gear set 36that is of the bevel gear planetary type as is hereinafter more fullydescribed. Casing 34 as illustrated includes a cup-shaped member 38 anda cap member 40 which each have peripheral flanges secured to each otherby circumferentially spaced bolts 42 that also secure a ring gear 44 ofthe bevel type which is rotatively driven by a bevel driving portion 46of the drive member 24.

With combined reference to FIGS. 1 and 2, the hydraulic coupling 32 alsoincludes a hydraulic pump 48 located within the casing 34 along therotational axis A and including a pumping component embodied by animpeller 50 having external teeth 52. The hydraulic pump also includesan internal ring gear 54 mounted by the casing 34 for rotationeccentrically with respect to the toothed impeller 50 and includinginternal teeth 56 of a number that is one more than the impeller teethand which are in a meshing relationship with the impeller teeth toprovide a pumping action upon relative rotation between the casing andthe toothed impeller. As is hereinafter more fully described, theimpeller 50 most preferably has six teeth 52 and the internal ring gear54 has seven teeth 56 which is a relationship that provides sufficientpumping capacity so that the hydraulic pump can act effectively as abrake while still having relatively constant pumping pressure withoutfluid pulsation that would adversely affect the hydraulic couplingprovided between the rotary members. As shown in FIG. 3, it is alsopossible for the hydraulic pump 48' to have its impeller 50' providedwith five external teeth 52' and for the ring gear 54' to have six teeth56' meshed with the impeller teeth which is a construction that willprovide a somewhat greater pumping capacity but less consistency in thefluid pressure but not so inconsistent as to interfere with effectivehydraulic coupling between the rotary members. Likewise as illustratedin FIG. 4, it is also possible for the hydraulic pump 48" to have itsimpeller 50" provided with seven internal teeth 52" and its internalring gear 54" to have eight teeth 56" when more consistent fluidpressure is desirable even though there is an accompanying decrease inthe amount of pumped fluid. Thus, the impeller has between five andseven external teeth with six being most preferable while the internalring gear has one more tooth than the number of impeller teeth utilized.

With combined reference to FIGS. 1, 5 and 6, the casing 34 has an inlet58 through which hydraulic fluid is pumped into the casing by thehydraulic pump 48. As illustrated in FIG. 1, there are actually two ofthe inlets 58 such that the pumping takes place in both directions ofrelative rotation between the rotary member embodied by the axle halfshaft 28 and the casing 34. In this connection, each of the inlets 58includes an associated check valve 60 for opening and closing inletbores 62 of varying size along the direction of 35 rotation. Each checkvalve 60 as shown in FIGS. 5 and 6 has a thin valve element 64 that ismounted by guides such as the threaded bolts 66 show for movementbetween the solid line indicated open position of FIG. 6 and the phantomline indicated closed position. Upon one direction of relative rotationbetween the impeller 50 and the internal gear 54 shown in FIG. 2, one ofthe check valves 60 opens to permit the hydraulic fluid to be pumpedfrom the housing 30 into the casing 34 while the other check valve 60 isthen closed so that the hydraulic fluid is not pumped out of the casingthrough the other inlet port. During the opposite direction of relativerotation between the impeller 50 and the casing 34, the open and closedpositions of the inlet ports 58 is reversed.

As illustrated in FIG. 1, a clutch 68 is received within the cup-shapedmember 38 of casing 34 adjacent the junction thereof with the cap member40 of the casing. Within the casing cap member 40, a pump housing insert70 is mounted and receives the hydraulic pump 48 as well as interfacingwith the clutch 68. This insert 70 has an annular piston chamber 71 thatreceives a clutch actuating piston 72 that engages the clutch 68 as ishereinafter more fully described to couple the casing 34 with the leftaxle half shaft 28 as is also hereinafter more fully described. Insert70 also has a wall defining a pair of transfer ports 74 through whichhydraulic fluid is pumped from the hydraulic pump 48 to the clutchactuating piston 72 within the piston chamber 71. This flow through thetransfer ports 74 is through one of the transfer ports upon onedirection of relative rotation between the impeller 52 and the ring gear54 and is through the other transfer port during the other direction ofrelative rotation between the impeller and the ring gear. Each of thetransfer ports 74 has an associated check valve 76 of a constructionthat is hereinafter more fully described in connection with FIGS. 15through 17. These check valves 76 ensure that the hydraulic fluid pumpedthrough either transfer port to the clutch actuating piston 72 is notpumped back into the hydraulic pump 48 through the other transfer port.

As best illustrated in FIGS. 7 and 9, an outlet port 78 is also providedand in the embodiment of FIG. 1 is located on the clutch actuatingpiston 72. A control valve 80 of the coupling is constructed inaccordance with the present invention and closes the outlet port 78 asis hereinafter more fully described when the pumped fluid reaches apredetermined pressure which is proportional to the relative rotationbetween the pump impeller and ring gear and thus corresponds to therelative rotation between the right axle half shaft 26 connected throughthe differential 36 to the casing 34 and the left axle half shaft 28that is connected to the impeller 50. As the pumped hydraulic fluidreaches the predetermined pressure, the valve 80 closes as ishereinafter more fully described to close the outlet port 78 and thusprevent the hydraulic fluid from being pumped from the hydraulic pump48. This causes the hydraulic pump 48 to act as a brake by coupling theimpeller 52 with the internal ring gear 54 and thereby also couples therotary members embodied by the right and left axle half shafts 26 and 28to each other.

As best illustrated in FIGS. 10 and 11, the valve 80 includes anelongated metallic strip valve element 82 having one portion or end 84that is mounted in a spaced relationship to the outlet port 78 in anysuitable manner such as by the headed bolts 86 illustrated. Valveelement 82 also has a distal end 88 that is movable between a solid lineindicated open position spaced from the outlet port 78 as shown in FIG.10 and a phantom line indicated closed position that closes the outletport. This valve element 82 is of the bimetallic type and thus includestwo metals 90 and 92 that have different coefficients of thermalexpansion so as to cause the valve element to move as its temperature israised and lowered. More specifically, as the hydraulic fluid is heatedsuch as during continued usage, the valve element end 88 moves towardthe outlet port 78 with the net result being that the less viscous fluidwill close the valve 80 at the same pressure of pumped fluidcorresponding to the same amount of relative rotation between the axlehalf shafts. Furthermore, upon cooling of the hydraulic fluid such asafter rest for a certain period of time, the valve element end 88 movesaway from the outlet port 78 such that the valve closes at the samepressure of pumping of the more viscous hydraulic fluid. Thus, thebimetallic valve element 82 compensates for viscosity changes as thehydraulic fluid is heated and cooled to ensure that the coupling betweenthe two rotary members embodied by the two axle half shafts takes placeat the same rate of relative rotation. More specifically, the valveclosing as discussed above causes the hydraulic pump 48 to then functionas a brake that limits the relative rotation between the two rotarymembers embodied by the two axle half shafts and also causes theactuation of the clutch 68 to further couple the two axle half shafts toeach other.

As best illustrated in FIGS. 10 and 11, the outlet port 78 preferablyincludes a main passage 94 that is closed by the valve element 82 as itsend 88 moves from the open position to the closed position as previouslydescribed. Outlet port 78 also includes a bleed passage 96 that remainsopen even when the valve element 82 is closed with respect to the mainpassage 94 in order to provide a bleed flow of hydraulic fluid thatcools the clutch 68 and also ensures that the temperature of thehydraulic fluid within the pump 48 does not excessively increase at arapid rate. When the valve element 82 opens, the fluid flow through bothpassages of the outlet port 78 provides cleaning of the bleed passage 96to remove any small particles that might block the smallercross-sectional flow area of the bleed passage. The control valve 80 isthus self cleaning during normal usage. Also, the bleed passage 96allows pressurized fluid to flow from the piston chamber 71 when thehydraulic pumping stops as the pair of rotary members cease to rotaterelative to each other, and the clutch 68 is disengaged as the pressurein the piston chamber drops as is hereinafter more fully described. Inthis construction of the control valve 80, the bleed passage 96 isdefined by the valve body provided by the piston 72 (FIG. 7) on whichthe valve element 82 is mounted.

As shown in FIGS. 7-11 and best illustrated in FIGS. 10 and 11, thecoupling includes an elongated mounting recess 98 having one portion orend 100 at which the one end 84 of the valve element 82 is mounted andhaving another end 102 at which the main passage 94 and bleed passage 96of the outlet port 78 are located. This recess in cooperation with thebimetallic valve element 82 provides a continually varying change in thecross-sectional flow area of flow to the outlet port 78 from the otherside of the valve element such that movement of the valve element end 88in response to temperature changes provides an accurate control of thepressure at which the valve element closes to initiate the operation ofthe hydraulic pump as a brake and the actuation of the clutch. For anygiven predetermined open position of the valve element 82, there is acertain pressure at which the hydraulic fluid of a certain velocity willcause closure of the valve element. This results from the flow of thehydraulic fluid between the valve element end 88 and the adjacent end ofthe recess 102 to the outlet port 78. This flow causes a pressure dropin the fluid upon passage past the valve element end 88 so that there isless force acting on the outlet side of the valve element end 88 than onthe hydraulic pump side which are respectively the lower and upper sidesas illustrated in FIG. 10. Movement of the valve element 82 to changethe position of its end 88 in response to temperature changes varies thecross-sectional area of flow between this valve element end and therecess end 102 so as to thereby accurately compensate for temperaturechanges and ensure that the closure of the valve 80 corresponds to thesame rate of relative rotation between the rotary members embodied bythe axle half shafts 26 and 28 shown in FIG. 1.

As best illustrated in FIGS. 7-9, the valve element 82 moves radiallywith respect to the axis A and recess 98 is located within an elongatedopening 103 that projects from the pump side of the piston 72 toward theclutch side of the piston. More specifically, the recess 98 is locatedwithin the opening 103 on the radial outward side thereof with respectto rotational axis A such that the distal valve element end 88 movesradially outward to the closed position and radially inwardly to theopen position as well as moving radially outward and inward to adjustfor temperature changes as previously described.

With reference to FIGS. 7-9, the hydraulic coupling is also illustratedas including a valve closure 104 that moves the valve element 82 to theclosed position with respect to the outlet port 78 upon rotation of thecoupling casing above a predetermined vehicle speed. This valve closureprovides the immediate coupling between the rotary members embodied bythe axle half shafts upon any relative rotation therebetween byoperation of the hydraulic pump as a brake as well as immediateactuation of the clutch in the manner previously described. This valveclosure 104 is preferably constructed to include a centrifical weight106 having a pivotal connection 108 that provides mounting thereof suchas on the piston 72 in the embodiment illustrated. The valve closure 104also includes an actuating portion 110 that extends from the centrificalweight 106 and engages the valve element 82 to move the valve element tothe closed position with respect to the outlet port 78 upon rotation ofthe coupling casing above the predetermined speed. More specifically,such rotation causes the centrifical force of the weight 106 to overcomethe resiliency of the valve element 82 and provide movement thereof fromthe open position to the closed position so that the braking actionprovided by the hydraulic pump and the clutch actuation are immediateupon any relative rotation between the rotary members embodied by theaxle half shafts as previously described.

With reference to FIG. 1, the hydraulic coupling 20 whose one rotarymember embodied by the right axle half shaft 26 is connected with thecasing 34 also has the clutch 68 previously described that extendsbetween the other rotary member embodied by the other axle half shaft 28and the casing. This clutch 68 includes alternating sets of clutchplates 112 and 114 with the one set of clutch plates 112 having outerperipheries with spline connections 116 to the casing 34, and with theother set of clutch plates 114 having a central opening with splineconnections 118 to the axle half shaft 28 which also has splineconnections 120 to the pump impeller 50 on the opposite side of theinsert 70 from the clutch. Pumped hydraulic fluid acting on the clutchpiston 72 as previously described compresses the sets of clutch plates112 and 114 to provide the coupling between the casing 34 and the rotarymember embodied by the axle half shaft 28. Pumped hydraulic fluid thatflows through the actuating piston 72 through the bleed passage of theoutlet port previously described then flows along the axle half shafts26 and 28 for passage out of the casing 34.

As previously mentioned, the hydraulic coupling 32 illustrated in FIG. 1has the planetary gear set 36 which is of the bevel gear type connectingthe casing 34 and the one rotary member embodied by the right axle halfshaft 26. This planetary gear set is positioned on the opposite side ofa casing wall 122 from the clutch 68 and includes a pair of side gears124 and 126 which have respective spline connections 128 and 130 to therotary members embodied by the axle half shafts 26 and 28. Planet gears132 of the gear set 36 are each meshed with the pair of side gears 124and 126 and are rotatably supported by a cross pin 134 that extendsthrough the rotational axis A between opposite sides of the casing 34.The planetary gear set 36 provides a differential action between therotary members embodied by the axle half shafts 26 and 28 until closureof the valve 80 causes the hydraulic pump 48 to function as a brake andalso actuate the clutch 68 as previously described whereupon the axlehalf shaft 26 is coupled through the spline connections 128, side gear124, planet gears 132, side gear 126 and the spline connections 130 withthe other axle half shaft 28.

With reference to FIG. 12, a related embodiment of the hydrauliccoupling is indicated by reference numeral 32a. This embodiment of thehydraulic coupling 32a has the same construction as the embodimentdisclosed in FIGS. 1-11 except as will be noted and thus has likereference numerals applied to like components thereof such that much ofthe previous description is applicable and thus need not be repeated.However, in this embodiment, there is no clutch as with the previouslydescribed embodiment such that the braking action provided by thehydraulic pump 48 provides the sole coupling between the impeller 50 andthe ring gear 54 and thus also the sole coupling between the pair ofrotary members embodied by the right and left axle half shafts 26 and28. In this embodiment, the casing cap member 40 has a pair of inlets 58located on opposite sides of the rotational axis A, with each beingprovided with an associated check valve 60 but only one being fullyshown and the other illustrated by a single phantom line schematicrepresentation. Furthermore, the casing cap member 40 also has a pair ofthe outlet ports 78 located on opposite sides of the rotational axis Awith each being provided with a control valve 80 of the sameconstruction previously discussed, but with only one outlet andassociated control valve being shown by full line representation and theother merely shown by a single phantom line schematic representation.Such provision of the pair of inlet ports and associated check valvesand the pair of outlet ports and associated control valves allows thebraking action provided by the hydraulic pump 48 to operate in bothdirections of relative rotation between the rotary members embodied bythe axle half shafts 26 and 28.

With reference to FIG. 13, another embodiment of the hydraulic couplingis indicated by 32b and includes components that are identical to thepreviously described embodiment except as will be noted such that likereference numerals are applied thereto and much of the previousdescription is applicable and need not be repeated. However, thehydraulic coupling 32b functions to provide four wheel driving and hasthe rotary member 26 provided with a fixed bolt connection 136 to thecasing 34. This rotary member 26 has a ring shape through which therotational axis A extends, and the other rotary member 28 has anelongated shape that extends through the casing 34 and through the ringshape of the one rotary member 26. The hydraulic pump 48 and clutch 68are located within the casing 34 and operate in the same manner as thepreviously described in connection with the embodiment of FIG. 1 exceptfor the fact that there is no associated planetary gear set. During use,the one rotary member 26 provides a take off for auxiliary axle drivingwhile the other rotary member 28 provides the driving between thevehicle engine and the primary drive axle. However, when there is adifference in rotational speed between the axles, the operation of thehydraulic coupling 32b then couples the axles to each other in the samemanner previously described in connection with the pump and clutchoperation.

With reference to FIG. 14, a further embodiment of the hydrauliccoupling 32c has a similar construction to the previously describedembodiment except as will be noted and thus has like reference numeralsapplied to like components thereof such that much of the previousdescription is applicable and need not be repeated. This embodiment ofthe hydraulic coupling 32c functions as a differential between two axlehalf shafts 26 and 28 driven by a rotary drive member 24 without anyplanetary gear set. Rather, each axle half shaft 26 and 28 has anassociated hydraulic pump 48 and clutch 68 like the previously describedembodiments. The clutches 68 are located adjacent each other andseparated as illustrated by a floating spacer 138. As such, actuation ofeither of the clutches 68 also actuates the other clutch to coordinatetheir operations with each other.

With reference to FIGS. 15 through 17, each transfer port 74 extendsthrough the insert 70 from the pump side toward the piston side and hasthe associated check valve 76 mounted on the piston side where thepiston is sealed between inner and outer annular flanges 142 and 144 byrespective O-rings 146 and 148. On the pump side, the transfer port 74has an enlarged shallow collection portion 150 that allows the pumpedhydraulic fluid to be received from different radial locations foreventual flow through the transfer port and the check valve 76 in thepiston side in order to provide the piston actuation as previouslydescribed. As best illustrated in FIGS. 16 and 17, each check valve 76includes a metallic strip valve element 152 having one end 154 mountedon the metallic insert by suitable fasteners 156 such as the headedbolts shown and has another distal end 158 that is normally biased tothe closed position of FIG. 16 by a resilient spring force of the valveelement. However, the pressurized fluid upon pumping acts against thespring bias to provide opening of the valve distal end 158 as shown inFIG. 17 to permit the fluid flow that moves the piston and actuates theclutch as previously described.

It should be noted that the cross-sectional flow area through thetransfer port 74 shown in FIG. 15 and the cross-sectional flow areathrough the open control valve 80 shown in FIGS. 9 and 10 are normallytuned to be approximately equal to each other as is also shown in FIG.27. Tuning of the coupling can also be performed as shown in FIG. 26 bymaking the cross-sectional flow area of the transfer port 74 smallerthan the cross-sectional flow area of the open control valve 80 to delaythe control valve closing and the consequent actuation of the clutch 68.Furthermore, faster control valve closing and consequent clutchactuation can be achieved by making the cross-sectional flow area of thetransfer port 74 larger than the cross-sectional flow area of the opencontrol valve 80 as shown in FIG. 28. In addition, it may also bepossible to tune the operation by controlling the closing spring bias ofthe transfer port valve element 152.

With reference to FIGS. 18 and 19, the piston 72 of the hydrauliccoupling is illustrated as having the control valve 80 mounted thereonas previously described and also is shown as having a coating 160 of anelastomeric rubber-like material, such as for example an ethyleneacrylic resin, on its one side which faces the hydraulic pump in theassembled condition. This coating 160 also defines outer and innerannular seals 162 and 163 for sealing with the adjacent outer and innerannular walls of the coupling to provide a slidably sealed relationship.This coating 160 is injection molded to a stamped steel plate 164 of thepiston 72 and also has positioning lugs 166 spaced circumferentiallyabout its periphery so as to protect the seal 162 when the piston movesto its full extent toward the left within the casing of the coupling.

With additional reference to FIGS. 20 and 21, the coating 160 isinjection molded to define the outlet port 78 with its main passage 94and bleed passage 96 previously described as well as to define themounting recess 98 in which the valve element 82 of the control valve 80is mounted as specifically shown in FIG. 21. Injection molding of thecoating facilitates the provision of the outlet port 78 with its mainpassage 94 and bleed passage 96. Furthermore, it should be noted thecoating 160 may have an annular portion 168 that extends through a holein the piston plate 164 to readily define the required cross-sectionalflow area of the main passage 94 of the outlet port 78 to thereby alsofacilitate tuning of the coupling as described above.

With reference to FIG. 22, another embodiment of the hydraulic couplingis indicated by 32d and includes components that are generally the sameas the previously described embodiments except as will be noted suchthat like reference numerals are applied thereto and much of theprevious description is applicable and need not be repeated. Thisembodiment of the hydraulic coupling has the wall of the casing insert70 that separates the hydraulic pump 48 and the clutch 68 provided withboth the transfer port 74 and the outlet port 78 extending therethroughas opposed to the prior embodiment wherein the outlet port extendsthrough the actuating piston of the clutch. This construction provides asupercharged circuit as described below.

More specifically as illustrated in FIGS. 23-25, two sets of transferand outlet ports 74 and 78 with associated check valves 76 and controlvalves 80 are provided with each set located within an associatecollection portion 150 on the pumped side of the insert wall throughwhich the ports extend. During one direction of relative rotationbetween the rotary members 26 and 28 (FIG. 2), the pumped hydraulicfluid flows from the hydraulic pump through the left transfer and outletports 74 and 78 shown in FIG. 25 to the piston chamber for flow to theright outlet port 78 back to the low pressure side of the pump asillustrated by the two solid line indicated arrows 170 and 172. Duringthe other direction of relative rotation between the pair of rotarymembers, the hydraulic fluid flows from the pump through the righttransfer and outlet ports 76 and 78 into the piston chamber for flow tothe left outlet port 78 as shown by the phantom line indicated arrows174 and 176. As such, there is a continual pumping during relativerotation between the pair of rotary members from the hydraulic pump tothe piston chamber 71 to provide actuation of the clutch 68 while thehydraulic fluid is then pumped back to the low pressure side of thehydraulic pump for further pressurization.

With the FIG. 22 embodiment of the hydraulic coupling 32d, there is noflow of the hydraulic fluid to the clutch plates 112 and 114. As such,it is desirable to have a lubricating passage 178 as shown for providinglubrication to the clutch plates. This lubrication passage 178 includespassage portions 180 and 182 through one of the rotary members 26 and apassage portion 184 through a connector 186 having spline connections188 to the rotary member 26 and also having the spline connections 118previously described to the clutch plates 114. Flow through thesepassage portions 180, 182 and 184 of the lubricating passage 178 from asuitable pumped source thus provides lubrication that functions as acoolant for the clutch plates 112 and 114 on the clutch plate side ofthe piston 72.

With reference to FIGS. 29-31, another version of the control valve 80eis illustrated and has the same construction as the previously describedcontrol valves except as will be noted such that like reference numeralsare applied to like components thereof and the prior description is thusalso applicable and will not be repeated. However, in this constructionof the control valve 80e, the distal end 88 of the elongated bimetallicstrip valve element 82 defines the bleed passage 96e of the port 78while the valve body provided by the piston 72 defines the main passage94 of the port 78. Thus, in the closed position illustrated by phantomline representation in FIG. 29, the bleed passage 96e allows pressurizedhydraulic fluid to bleed through the port 78 as with the previouslydescribed embodiment and, upon opening of the valve element 82 asillustrated by solid line representation, the bleed passage 96e iscleaned of any accumulation by the fluid flow in the same manner aspreviously described. The operation of both valve constructions is thussimilar.

Each of the embodiments of the control valve described above has itscontrol valve element 82 provided with the distal end 88 thereofextending in an inclined relationship with respect to its mounting end84 in the opened position of the valve. This inclined relationship isprovided by a bend in the control valve element adjacent its mountingend 84. Upon movement to the closed position, the control valve element82 assumes a generally flat shape.

With reference to FIGS. 32-38, further embodiments of the control valveare illustrated and have much of the same construction as the previouslydescribed control valves except as will be noted. As such, likereference numerals are applied to like components thereof and most ofthe prior description is thus also applicable and will not be repeated.

As illustrated in FIGS. 32 and 33, another embodiment of the controlvalve 80f includes a valve body 190 that is preferably injection moldedfrom a suitable plastic and has one portion or end 100 at which the oneportion or end 84 of the elongated valve element 82 is mounted by thefastener bolts 86 and has an end 102 at which the main passage 94 of theport 78 extends through the valve body. The valve element 82 isgenerally flat between its one portion 84 and its distal end 88. Recess98 of the valve body 190 has a greater depth at the end 102 thereof thanat the one portion provided by its end 100 and is inclined therebetween.As such, the control valve 80f is open with the flat valve element 82mounted within the recess 98 and is closed by movement of the distal end88 of the valve element toward the port 78 in the same manner previouslydescribed in connection with the bleed flow through the bleed passage96.

With continuing reference to FIG. 32, a connector 192 of the controlvalve 80f is provided for securing the valve body 190 for use such as tothe piston 72 as illustrated with a port portion 78' aligned with theport 78 of the valve body. This connector 192 as illustrated is embodiedby a suitable plastic film 194 with a suitable adhesive on each sidethereof so as to secure the valve body 190 within a recessed hole 196 ofthe piston 72. The film 194 may be die stamped to the required shapewhich as shown in FIG. 33 includes a port opening 78".

Best results with the control valve 80f are achieved when the recess 98has a curved surface 198 providing the inclination between its oneportion 100 and its end 102. Thus, the elongated control valve 82 movesinto and out of engagement with the curved surface 198 by a continuouslymoving line as it is moved between the open and closed positions withrespect to the port 78.

With reference to FIG. 34, another embodiment of the control valve 80f'has the same construction as the embodiment of FIGS. 32 and 33 exceptfor the fact that its connector 192 instead of being a piece of doublesided adhesive film is provided by at least one mechanical fastener200,202. As illustrated, there is one fastener 200 through which theport 98 extends and which has a headed end 204 for providing a snapconnection to the piston 72 through the piston port 78'. Furthermore,the other fastener 202 illustrated is located adjacent the recessmounting portion 100 extending through a hole 205 and has a snapconnector end 206 for providing securement of the valve body 190 inposition.

It should be appreciated that each of the embodiments illustrated inFIGS. 29-34 while illustrated for use on the piston 72 can also bemounted on the wall 70 for use in the supercharged circuit asillustrated in FIG. 25. Furthermore, each of the previously describedelongated valve elements 82 has its elongated configuration provided bya straight shape although this elongated configuration can also beprovided by a curved shape such as with the valve 76 shown in FIG. 25and as is hereinafter more fully described in connection with theembodiments of FIGS. 35-38.

With reference to FIG. 35, another embodiment of the control valve 80gis constructed to function in the supercharged circuit as previouslydescribed in connection with FIG. 25 but provides control of both ports78 through the coupling wall for flow back to the hydraulic pump. Morespecifically, the valve body 190 of this embodiment of the control valvehas an elongated mounting recess 98 of a curved shape including oppositeends 102 and a curved intermediate portion 100 extending between itsends. The valve element 82 is generally flat like the embodiments ofFIGS. 32-34 and has a pair of opposite distal ends 88 as well as acurved intermediate portion 84 extending between its ends. This curvedintermediate portion 84 of the control valve element 82 is mountedwithin the recess 98 at the curved intermediate portion 100 thereof bythe threaded fastener bolts 86. Both ports 78 have the same constructionas each other with a main passage 94 and a bleed passage 96 thatfunction as previously described adjacent the associated ends 102 of therecess 98. This recess 98 has a greater depth at each end 102 thereofthan at the intermediate portion 100 and is inclined from each endthereof to its intermediate portion as illustrated in FIG. 37. Thisinclination is preferably provided by a pair of curved surfaces 198 suchthat each distal end 88 of the flat valve element 82 moves by acontinually moving line into and out of engagement with the associatedcurved surface upon movement between the open and closed positions withrespect to the associated port 78.

As illustrated in FIG. 37, the control valve 80g has a connector 192that is embodied by a double-sided adhesive plastic film 194 like thepreviously described embodiment of FIGS. 32 and 33. Likewise, while thevalve body 198 is preferably a plastic injection molding made from asuitable plastic or a die casting made from steel or aluminum, otherways of manufacturing the valve body are possible.

As illustrated in FIG. 38, another embodiment of the control valve 80g'has the same construction as the control valve 80g of FIGS. 35-37 buthas its connector 192 embodied by a pair of the mechanical fasteners 200like the control valve element of FIG. 34. As such, these mechanicalfasteners 200 extend through suitable port portions 78' in the couplingwall 70 such that the control valve provides a control of the flow backto the pump in the manner previously described in connection with FIG.25.

It should be appreciated that each of the embodiments of FIGS. 32-38while illustrated with the valve body 190 as an injection molding couldalso be constructed as part of the piston or the coupling wall thatprovides part of the piston housing in the broadest aspect of theinvention. However, particular advantages are achieved by the injectionmolding of the valve body as specifically disclosed.

It should also be appreciated that each of the embodiments wherein thebleed passage 96 is illustrated as being part of a valve body could alsohave the bleed passage constructed as part of the distal end 88 of theassociated valve element 82 like the embodiment of FIGS. 29-31.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternatives, designs and embodiments forpracticing the present invention as defined by the following claims.

What is claimed is:
 1. A hydraulic coupling for with a vehicledrivetrain within a housing thereof containing hydraulic fluid torotatively couple a pair of rotary members about a rotational axis, thehydraulic coupling comprising: a casing of a hollow construction that isrotatable within the housing about the rotational axis; a hydraulic pumplocated within the casing along the rotational axis to provide a pumpingaction upon relative rotation between the two rotary members; an inletport through which hydraulic fluid is pumped into the casing by thehydraulic pump; a clutch including a piston chamber located within thecasing and having an actuating piston that is received within the pistonchamber and actuatable to engage the clutch and couple the two rotarymembers to each other; the casing including a transfer port throughwhich the pumped hydraulic fluid is fed from the hydraulic pump to thepiston chamber; an outlet port through which pumped hydraulic fluidflows from the piston chamber; and a control valve including atemperature compensated valve element movable between an open positionspaced from the outlet port and a closed position that closes the outletport when the pumped fluid reaches a predetermined pressure to actuatethe piston and engage the clutch to thereby rotatively couple the pairof rotary members to each other.
 2. A hydraulic coupling as in claim 1wherein the valve element comprises an elongated strip valve elementhaving one portion that is mounted in a spaced relationship to theoutlet port and having a distal end that is movable between the openposition spaced from the outlet port and the closed position that closesthe outlet port.
 3. A hydraulic coupling as in claim 2 wherein theoutlet port includes a main passage that is closed by the valve elementand a bleed passage through which pumped hydraulic fluid bleeds with thevalve element closed, and an elongated mounting recess having one end atwhich the one portion of the valve element is mounted and having anotherend at which the main passage and bleed passage of the outlet port arelocated.
 4. A hydraulic coupling as in claim 1, 2 or 3 wherein theoutlet port extends through the actuating piston, and the control valvebeing mounted on the actuating piston to control pumped hydraulic fluidflow through the piston.
 5. A hydraulic coupling as in claim 1 or 2wherein the outlet port extends through the actuating piston, thecontrol valve being mounted on the actuating piston to control pumpedhydraulic fluid flow through the piston, the piston having a coatingthat defines a seal for slidably engaging with the piston chamber, andthe outlet port including a main passage and also including a bleedpassage that is defined by the piston coating and that allows pumpedhydraulic fluid to flow through the piston with the valve elementclosed.
 6. A hydraulic coupling as in claim 1, 2 or 3 wherein the casingincludes a wall that separates the hydraulic pump and the piston chamberthat receives the actuating piston of the clutch, with the transfer portextending through the casing wall to feed the pumped hydraulic fluidfrom the hydraulic pump to the clutch actuating piston within the pistonchamber, and with the outlet port also extending through the casing walland under the operation of the control valve feeding the pumpedhydraulic fluid from the piston chamber back through the casing wall tothe hydraulic pump to provide a supercharged circuit.
 7. A hydrauliccoupling as in claim 6 further including a lubricating passage forsupplying a lubricating fluid to the clutch to function as a coolant. 8.A hydraulic coupling as in claim 1 wherein the transfer port into thepiston chamber from the hydraulic pump has a smaller cross-sectionalarea than the outlet port from the piston chamber such that the clutchactuation is delayed by restricting the flow of pumped hydraulic fluidthrough the transfer port while the hydraulic pump functions as a braketo limit rotation between the pair of rotary members.
 9. A hydrauliccoupling as in claim 1 wherein the transfer port into the piston chamberfrom the hydraulic pump has about the same cross-sectional area as theoutlet port from the piston chamber such that both the transfer port andthe outlet port restrict the flow of pumped hydraulic fluid about thesame as each other.
 10. A hydraulic coupling as in claim 1 wherein thetransfer port has a larger cross-sectional area than the outlet portsuch that the transfer port does not restrict the flow of pumpedhydraulic fluid into the piston chamber so that the clutch actuation isnot delayed by the transfer port.
 11. A hydraulic coupling for use witha vehicle drivetrain within a housing thereof containing hydraulic fluidto rotatively couple a pair of rotary members about a rotational axis,the hydraulic coupling comprising: a casing of a hollow constructionthat is rotatable within the housing about the rotational axis; aplanetary gear set that connects the casing with the pair of rotarymembers; a hydraulic pump located within the casing along the rotationalaxis to provide a pumping action upon relative rotation between the tworotary members; an inlet port through which hydraulic fluid is pumpedinto the casing by the hydraulic pump; a clutch including a pistonchamber located within the casing and having an actuating piston that isreceived within the piston chamber and actuatable to engage the clutchand couple the two rotary members to each other; the casing including atransfer port through which the pumped hydraulic fluid is fed from thehydraulic pump to the piston chamber; the casing also including anoutlet port through which pumped hydraulic fluid flows from the pistonchamber; and a control valve including a temperature compensated valveelement movable between an open position spaced from the outlet port anda closed position that closes the outlet port when the pumped fluidreaches a predetermined pressure to actuate the piston and engage theclutch to thereby rotatively couple the pair of rotary members to eachother through the planetary gear set.
 12. A hydraulic coupling for usewith a vehicle drivetrain within a housing thereof containing hydraulicfluid to rotatively couple a pair of rotary members about a rotationalaxis, the hydraulic coupling comprising: a casing of a hollowconstruction that is rotatable within the housing about the rotationalaxis; a planetary gear set that connects the casing with the pair ofrotary members; a hydraulic pump located within the casing along therotational axis and including an impeller rotatively connected to one ofthe rotary members and having external teeth; the hydraulic pump alsoincluding an internal ring gear mounted by the casing for rotationeccentrically with respect to the toothed impeller and includinginternal teeth of a number one more than the impeller teeth and in ameshing relationship therewith to provide a pumping action upon relativerotation between the casing and the toothed impeller; an inlet portthrough which hydraulic fluid is pumped into the casing by the hydraulicpump; a clutch including a piston chamber located within the casing andhaving an actuating piston that is received within the piston chamberand actuatable to engage the clutch and couple the two rotary members toeach other; the casing including a transfer port through which thepumped hydraulic fluid is fed from the hydraulic pump to the pistonchamber; the casing also including an outlet port through which pumpedhydraulic fluid flows from the piston chamber; the outlet port includinga main passage and a bleed passage; and a control valve including atemperature compensated valve element movable between an open positionspaced from the outlet port and a closed position that closes the mainpassage of the outlet port when the pumped fluid reaches a predeterminedpressure to actuate the piston and engage the clutch to therebyrotatively couple the pair of rotary members to each other withtemperature compensation provided by the valve element of the controlvalve and with the bleed passage allowing hydraulic fluid to flow fromthe piston chamber.
 13. A hydraulic coupling for use with a vehicledrivetrain within a housing thereof containing hydraulic fluid torotatively couple a pair of rotary members about a rotational axis, thehydraulic coupling comprising: a casing of a hollow construction that isrotatable within the housing about the rotational axis; a pair ofhydraulic pumps located within the casing along the rotational axis andincluding respective impellers rotatively connected to the pair ofrotary members and having external teeth; each hydraulic pump alsoincluding an internal ring gear mounted by the casing for rotationeccentrically with respect to the toothed impeller thereof and includinginternal teeth of a number one more than the impeller teeth and in ameshing relationship therewith to provide a pumping action upon relativerotation between the casing and the toothed impeller; a pair of inletports through which hydraulic fluid is respectively pumped into thecasing by the pair of hydraulic pumps; a pair of clutches thatrespectively extend between the casing and the pair of rotary members,each clutch including an associated piston chamber located within thecasing and having an actuating piston that is received within the pistonchamber thereof and actuatable to engage the clutch and couple thecasing and the two rotary members to each other; the casing including apair of transfer ports through which the pumped hydraulic fluid is fedfrom the pair of hydraulic pumps to the associated piston chambers; thecasing also including a pair of outlet ports through which pumpedhydraulic fluid flows from the pair of piston chambers; a pair ofcontrol valves respectively associated with the pair of outlet ports;and each control valve including a valve element movable between an openposition spaced from the associated outlet port and a closed positionthat closes the associated outlet port when the pumped fluid reaches apredetermined pressure to actuate the associated piston and engage theassociated clutch to thereby rotatively couple the pair of rotarymembers to each other.